This invention relates to controlling bypass flow of a fixed displacement pump internally in response to external load and flow requirements in a load responsive system.
A more particular aspect of the invention is the internal pump control, of pump discharge pressure to low unload pressure near atmosphere, in the standby load responsive condition via a single signal from said load responsive system.
Load sensed directional control valves with load sensing bypass flow controls have greatly reduced the system input horsepower requirements in systems using fixed displacement pump. A typical type of this direction control valve with bypass can be seen in the United States patent issued to Haussler U. S. Pat. No. 3,488,953 and U.S. Pat. Nos. 3,882,896 and 4,159,724 issued to Budzich. Although these valves have greatly increased the system efficiency these types of valves do dictate a load sensed pressure equal to the delta P of the bypass flow control in the neutral or standby condition. This pressure can exceed a value of 200 psi and depending on the discharge volume of the pump represent a high energy loss in the standby mode. This type of valve, due to the nature of it being a directional type control valve, is usually physically installed in a system a great distance from the fixed displacement pump and near the actual load. This situation causes the pressure drop to vary by the length of line or pressure conduit and number of restrictions due to fittings and pipe bends between the fixed displacement pump and the valve. This pressure drop depending on the good wishes of the user can amount to a pressure greater than 200 psi. The doubling of the previously mentioned 200 psi across the valve bypass control relates to a 400 psi pump pressure drop and although the standby drop constitutes a significant loss in efficiency within this type of valve, it is doubled when added to the line loss seen in the interconnecting lines from the fixed displacement pump to the valve.
My patent application Ser. No. 07/008,313, filed Jan. 29, 1987, now abandoned, shows the integration of two controls internal within the fixed displacement pump accomplishing the low unload standby and load sensing bypass control and resulting in a minimum savings in horsepower of 50% using a single load responsive signal. The Budzich U.S. Pat. No. 4,789,126, filed Mar. 23, 1987 and issued Jan. 17, 1989, shows a low unload load responsive pump control. However, the said line losses and the requirement of an auxiliary pump to function the low unload causes a minimal increase of efficiency in reference to Haussler. Although my earlier patent application reduced horsepower draw by over 50% in reference to the Haussler or Budzich patents, the dual controls for bypass and low unload contained internally within the fixed displacement pump and where connected to the pump discharge volute passage in a parallel teed drilling resulting in a flow path incorporating a 90 degree flow path alteration. This change in fluid flow direction resulted in a fractional horsepower draw.